Tim Zahns original Thrawn Trilogy is the best by a long way. The follow up's, the Hand of Thrawn were disappointing.
The next best read is probably the Rogue Squadron graphic novels, which are also written by Michael Stackpole for the most part but work much better than the books. The Tales of the Jedi graphic novels are also great if you can find them.
The Corellian trilogy and the Black Fleet Crisis are both readable.
Avoid the Crystal Star like the plague.
If you like the Thrawn trilogy I reccommend The Icarus Hunt and The Conquerers books which are also by Tim Zahn.